1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium that includes two or more recording layers, its manufacturing method, and a magnetic storage apparatus that includes the perpendicular magnetic recording medium.
2. Description of the Related Art
In recent years and continuing, magnetic storage apparatuses that include a perpendicular magnetic recording medium attract attention for the medium's high-density recording capability compared with a conventional in-plane magnetic recording medium (longitudinal magnetic recording medium). The perpendicular magnetic recording medium records information by perpendicularly magnetizing a recording bit (magnetic domain) that is formed on a surface of a recording layer, wherein adjacent recording bits are arranged non-parallel to each other.
As for the perpendicular magnetic recording medium, the so-called “heat fluctuation” associated with high-density recording is a problem. With the heat fluctuation, recorded information is lost because the number of magnetic domains is decreased. In order to realize a recording medium that can stand the heat fluctuation, a ferromagnetic material having great magnetic anisotropic energy Ku is necessary, or alternatively a great volume of the magnetic domain is required. Further, if the magnetic anisotropic energy Ku is great, the intensity of a recording magnetic field has to be great.
Further, if the volume of the magnetic domain is great for high-density recording, the thickness of the magnetic film has to be great. If the thickness of the magnetic film is great, the intensity of the recording field has to be great, posing a problem in that transitional noise is increased due to flattening of the slope of the recording field intensity in an in-plane direction. As described above, measures against the heat fluctuation are desired wherein satisfactory saturation recording characteristics are obtained.
An attempt to solve the problem is made by structuring the recording layer with a multilayer of two or more layers. The attempt aims at improving the recording characteristics by laminating the recording layers having different magnetic anisotropy. However, the intensity of the recording field generated by a head has to be great even if the number of the layers is two.
In view of the above, a magnetic recording medium called an Exchange Coupled Composite (ECC) medium is proposed. The ECC is a perpendicular magnetic recording medium. The recording layer of the ECC includes two or more magnetic layers having different directions of magnetization easy domain. According to the ECC, it is expected that thermal stability will be obtained while the intensity of the recording field is reduced and side erasing is reduced (for example, Patent Reference 1).
Patent Reference 1 discloses a perpendicular magnetic recording medium including a first recording layer and a second recording layer, wherein the first recording layer includes magnetic particles perpendicularly arranged to a film surface, and the second recording layer includes magnetic particles that are inclined in a direction of a track width. Here, the second recording layer is formed by depositing sputter particles that come in a predetermined angle range, while other sputter particles are intercepted by a shield plate. Therefore, the sputter particles are wastefully consumed, and depositing speed is slow.
[Patent reference 1] JPA 2005-302150